The present invention relates to a humidity sensor, the electric resistance of which varies in response to the variance of humidity in an atmosphere.
Heretofore, various kinds of humidity sensors the electric resistance of which varies in response to the variance of humidity in an atmosphere have been known. However, they have drawbacks as mentioned below.
That is:
(1) a humidity sensor impregnated with an electrolyte salt such as lithium chloride etc.;
The humidity detection range of this humidity sensor is narrow. In addition, the life of this humidity sensor becomes extremely short in a high humidity atmosphere due to the fact that the electrolyte salt is diluted.
(2) a humidity sensor using a resin of humidity-absorbing nature into which an electrically conductive powder is mixed:
This humidity sensor is unable to detect a low humidity. In addition, this humidity sensor is inferior in its yield when it is produced as well as in its nature when it is used for a long period of time.
(3) a humidity sensor the surface of which is made of a metal oxide, e.g. aluminum oxide etc.:
This humidity sensor entails hysteresis and a reduction in sensitivity if the relative humidity becomes not less than 80%. In addition its nature deteriorates very rapidly in a high humidity atmosphere.
(4) a humidity sensor using a metal oxide:
The resistance of this humidity sensor is increased as time goes on and its nature varies in response to the changes in temperature. In addition, its manufacturing method becomes complex.
(5) a humidity sensor using a hydrophilic high molecular substance:
The "hydrophilic high molecular substance" means, for example, polyvinyl alcohol, polyvinyl acetate, polyvinyl pyrrolidone etc., which are soluble in water and the characteristic nature of which speedily deteriorates. This humidity sensor, which is used with its surface covered and mainly together with a semiconductor, is difficult to manufacture so as to have uniform characteristics. In addition, its characteristics are not stable and its life is short.